In the past, impellers, expanders, turbines and other high-speed rotational devices have suffered from the effects of stress cracking and failure, wobbling or uncentering of the mass of the device and displacement problems occurring when the mass of the rotating device migrates radially outward (elastic deformation) under the influence of centrifugal force during high speed operation.
Attempts have been made to secure such rotational devices to their respective drive shafts to avoid these drawbacks yet at the same time insure transmission of torque between the drive shaft and the rotational device. Various uses of splines, keys and locating pins have been utilized, but most of such fastenings have created points of stress concentration such as occur when restricting the outward concentric or eccentric migration of the rotational device during high speeds.
The prior art has made various attempts to secure rotational devices of significant mass to an axle or drive shaft so as to provide positive rotational engagement of the device. Numerous attempts have been made to overcome the problems attendant with providing positive rotational engagement while preventing stress crack failure and accommodating for the known distortion and concentric migration of large mass devices undergoing significant rotational and therefore centrifugal forces and other dynamic stresses, such as hoop stress.
In U.S. Pat. No. 892,932 a mounting means is provided for a drive gear and a sprocket gear wherein a pin is positioned in a slot which is fabricated with one-half of its diameter in one gear and the other half of its diameter in the second gear. A portion of the pin is entirely set within the first gear.
U.S. Pat. No. 3,995,968 discloses a turbine rotor and disc assembly in which a pin is placed at the interface of the disc and rotor. A bushing is not provided between the rotor and the disc.
In U.S. Pat. No. 3,077,334 the problem of dynamic stress in high-speed turbine wheels is documented. However, the recited solution to the problem regarding dynamic stress in the turbine wheel is the use of radially aligned pins placed at the outermost edges of the turbine wheel bore.
U.S. Pat. No. 3,368,833 discloses the mounting of a drive wheel on a bushing by the utilization of a combination of threaded screws of long configuration and of short tapered configuration. The screws are designed to apply significant pressure respectively axially and radially on the bushing and drive wheel assembly. The frictional fit between the bushing and drive wheel is provided by the forced action of the screws against the tapered fit of the former elements.
In U.S. Pat. No. 4,220,372 a wheel and axle assembly is disclosed which utilizes a combination of pins and bolts to secure a wheel hub to an axle by means of a clamping bushing element. However, the bolts fully immobilize the hub with respect to the axle and the bushing in this low speed application of wheel mounting technology.
Finally in U.S. Pat. No. 1,873,956 the problem of rotor expansion under high-speed conditions is recognized, but the use of a spring steel element to secure the rotor to the axle is taught rather than a shrink or interference fit in combination with axial pins.
The present invention overcomes the short comings of the prior art by the use of a combination of an interference fit in the low-stress area of a high-speed turbo disc-bushing interface, as well as the placement of torque pins in such an interface to preclude radial containment of the disc and to diminish concentrations of dynamic stress in the disc mass while at the same time preventing eccentric migration of the disc. This invention further stabilizes the mounting assembly of a turbo disc by fully encasing the torque pins, which provide positive rotational engagement, within the flange of a bushing in the vicinity of greatest dynamic stress of the turbo disc mass.
The unique mounting assembly of the present invention provides: (a) transmission of torque to and from the turbo disc with positive engagement without detrimental stress concentration; (b) adequate centering, both static and dynamic, of the turbo disc on the drive shaft by utilization of the bushing of the present invention intermediate of the turbo disc and the drive shaft; and (c) ease of assembly of the turbo disc onto the shaft without the need to disturb the torque pins in their placement. Additionally, the mounting assembly can be fabricated without special tools by simple drill press and lathe equipment.